The synthesis of molecules having the general formula GXAsR2 is being carried out. G is a biochemical moiety such as a monosaccharide, an amino acid, a di- or oligopeptide, a purine or pyrimidine, a lipid, such as cholesterol or lipoic acid, etc. X is a sulfur or selenium atom. More than 20 of these derivatives have been found to exhibit carcinostatic activity in vitro in the KB test system and in vivo in the PS and LE test systems. The purpose of the research is to enhance this activity by a synergistic approach. The XAsR2 will be incorporated into molecules in which G has already been shown to possess useful carcinostatic activity. For example, G can be thymidine, 5-thioglucose, testosterone, estradiol-17 beta, etc. Concurrently, the kinetics of the reaction between arsenic(V) and thiol containing biomolecules are being studied. These investigations will subsequently be extended to include thiol containing enzymes as substrates. Such studies can be useful in understanding the biochemical action of arsenic compounds.